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Soluble Sugars and Free Amino Acids of Poa pratensis Exposed to Chlorophenoxy Herbicides and Pathogenesis by Drechslera sorokiniana. James P. Madsen, Postdoctoral research fellow, Department of Agronomy, University of Kentucky, Lexington 40546-0091; Clinton F. Hodges, professor of horticulture and of plant pathology, Department of Horticulture, Iowa State University, Ames 50011. Phytopathology 73:737-740. Accepted for publication 24 November 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-737.

The influence was evaluated of two postemergence herbicides, 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP) and 2-(2,4,5-trichlorophenoxy) propionic acid (2,4,5-TP), on total and individual soluble sugars and free amino acids of leaves of herbicide-tolerant Poa pratensis and on the severity of leaf spot induced by Drechslera sorokiniana. The incidence of leaf spot of plants growing in soil treated with MCPP was more severe than leaf spot of the untreated controls. 2,4,5-TP had no influence on the severity of the leaf spot. Leaves of plants growing in soil treated with either herbicide had lower sucrose and total sugar amounts than did control leaves. The decrease in sucrose and total soluble sugars in uninoculated leaves of herbicide-treated plants was significantly correlated with increased leaf spot severity of inoculated leaves of herbicide-treated plants. No differences existed in sugar content among infected leaves of control or herbicide-treated plants. The results are discussed relative to previous classification of Drechslera leaf spot on P. pratensis as a “low sugar” disease. MCPP and 2,4,5-TP had little effect on the total free amino acids in uninoculated leaves. Inoculated leaves of control and MCPP-treated plants had greater amounts of total free amino acids than did uninoculated leaves of respective plants. No difference existed in total free amino acid content between uninoculated and inoculated leaves of 2,4,5-TP-treated plants. No meaningful significant correlations existed between free amino acid content and leaf spot severity.

Additional keywords: Bipolaris sorokinianum, Helminthosporium sativum, Kentucky bluegrass, mecoprop, silvex.